Haxl.Core.Memo

Most users should import Haxl.Core instead of importing this module directly.

Documentation

memo :: (Typeable a, Typeable k, Hashable k, Eq k) => k -> GenHaxl u a -> GenHaxl u a

Memoize a computation using an arbitrary key. The result will be calculated once; the second and subsequent time it will be returned immediately. It is the caller's responsibility to ensure that for every two calls memo key haxl, if they have the same key then they compute the same result.

memoFingerprint :: Typeable a => MemoFingerprintKey a -> GenHaxl u a -> GenHaxl u a

data MemoFingerprintKey a where

A memo key derived from a 128-bit MD5 hash. Do not use this directly, it is for use by automatically-generated memoization.

Constructors

MemoFingerprintKey :: !Word64 -> !Word64 -> Addr# -> Addr# -> MemoFingerprintKey a

Instances

Eq (MemoFingerprintKey a)

Methods

(==) :: MemoFingerprintKey a -> MemoFingerprintKey a -> Bool

(/=) :: MemoFingerprintKey a -> MemoFingerprintKey a -> Bool

Hashable (MemoFingerprintKey a)

Methods

hashWithSalt :: Int -> MemoFingerprintKey a -> Int

hash :: MemoFingerprintKey a -> Int

memoize :: GenHaxl u a -> GenHaxl u a

Transform a Haxl computation into a memoized version of itself.

Given a Haxl computation, memoize creates a version which stores its result in a MemoVar (which memoize creates), and returns the stored result on subsequent invocations. This permits the creation of local memos, whose lifetimes are scoped to the current function, rather than the entire request.

memoize1 :: (Eq a, Hashable a) => (a -> GenHaxl u b) -> GenHaxl u (a -> GenHaxl u b)

Transform a 1-argument function returning a Haxl computation into a memoized version of itself.

Given a function f of type a -> GenHaxl u b, memoize1 creates a version which memoizes the results of f in a table keyed by its argument, and returns stored results on subsequent invocations with the same argument.

e.g.:

allFriends :: [Int] -> GenHaxl u [Int] allFriends ids = do memoizedFriendsOf <- memoize1 friendsOf concat $ mapM memoizeFriendsOf ids

The above implementation will not invoke the underlying friendsOf repeatedly for duplicate values in ids.

memoize2 :: (Eq a, Hashable a, Eq b, Hashable b) => (a -> b -> GenHaxl u c) -> GenHaxl u (a -> b -> GenHaxl u c)

Transform a 2-argument function returning a Haxl computation, into a memoized version of itself.

The 2-ary version of memoize1, see its documentation for details.